The invention relates to actuators useful in robotic applications, and more particularly to actuators capable of providing very large forces, for example, 500 pounds, to control movement of a driven member with a very high degree of precision, for example, with 1 mil precision. The invention more particularly relates to improvements in air-over-hydraulic systems and digital control valves therefor, and to improved methods and apparatus for energizing the pneumatic cylinders.
There are numerous industrial and scientific applications for devices capable of applying a very large force, for example, a several hundred pound force, to a driven member in such a manner as to produce very precise control of the position of the driven member, for example, to within one-thousandth of an inch (i.e., 1 mil). At the present state of the art, pneumatic and/or hydraulic systems, especially inexpensive ones, are incapable of accomplishing this objective. Ordinarily, mechanical systems utilizing gears, jackscrews, screw gears and the like must be utilized when such large forces are to be applied with such high precision to a driven member. Various so-called air-over-hydraulic or air-over-oil systems are well-known, wherein an "active" pneumatic cylinder is utilized to apply a large force to a driven member, and a "passive" hydraulic cylinder is utilized to control the movement of the driven member. Typically, an electronically actuated valve is utilized to allow oil in the hydraulic cylinder to bleed in a controlled manner from one side of the piston of the hydraulic cylinder to the other and thereby limit and/or control the movement of the driven member to which the force is being applied by the pneumatic cylinder. The state of the art is believed to be accurately represented by U.S. Pat. Nos. 4,528,894 (Crosby), 3,176,801 (Huff), and 2,775,015 (Erb). However, none of the air-over-hydraulic systems disclosed in these references have the capability of controlling movement of a member driven by a force as large as 500 pounds with locational precision as nearly as accurate as 1 mil.
There are various applications for actuators capable of applying such large forces to a driven member with 1 mil locational precision, wherein leakage of air vented from pneumatic cylinders is unacceptable. There also are applications wherein utilization of an external bulky source of compressed air to energize a hydraulic cylinder is unacceptable.
There are yet other applications wherein there is a need to provide a minute, precise "forced adjustment" of an already-positioned driven member.
It would be desirable to provide a low cost actuator that is light in weight, and is only about 15 inches by 4 inches by 4 inches in size, yet is capable of providing a controlled force as high as about 500 pounds with precision of at least approximately 1 mil.
Although the prior art discloses a variety of basic mechanical pneumatic and hydraulic elements, no suitably accurate digital valve and technique for combining it with an air-over-hydraulic system has been provided that is capable of achieving locational positioning of a driven member to which forces as high as hundreds of pounds are applied with 1 mil accuracy.